From: Eero Saynatkari <ruby-ml@...>
Date: 2009-03-19T00:33:52+09:00
Subject: [ruby-core:22928] Re: [Bug #1301] Poor RegExp Matching Performance

Excerpts from Marius M��rnes Mathiesen's message of Wed Mar 18 16:53:08 +0200 2009:
> Bug #1301: Poor RegExp Matching Performance
> http://redmine.ruby-lang.org/issues/show/1301
> 
> Author: Andreas Grau
> Status: Open, Priority: Normal
> Category: core
> ruby -v: 1.9.0 (2008-06-20 revision 17482) [i486-linux]
> 
> I noticed a very poor performance on matching regular expressions.

You mean non-matching? Aside from which, I would be hard-pressed
to call the code below a "regular expression."

> Running following code using ruby 1.9.0 on a Core2Duo (2x2Ghz) takes more than
> 20s to complete.
> 
> regexp = /[b]+.+.+.+.+.+.+.+.+[a]/
> str="bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
> regexp.match(str)

Are you able to produce a reasonable example of where this
is a problem and not just a pathologically horrible regexp?
The above, written as:

    /[b]+.+[a]/

Or:

    /[b].+.{1,}[a]/

Completes instantly.


--
Magic is insufficiently advanced technology.